Binary blends of styrene/acrylonitrile copolymer and butyl acrylate/acry-lonitrile copolymer and methods for preparing the same



United States Patent 3,118,855 BINARY BLENDS 0F STYRENE/ACRYLONITRILECOPOLYMER AND BUTYL ACRYLATE/ACRY- LONITRILE COPOLYMER AND METHODS FORPREPARING THE SAME James A. llerblg and lval O. Salyer, Dayton, Ohio,as-

signors to Monsanto Chemical Company, St. Louis, Mo., a corporation ofDelaware No Drawing. Filed July 21, 1960, Ser. No. 44,284 12 Claims.(Cl. 260-455) This invention relates to styrene/acrylonitrilecopolymers. in one aspect, this invention relates to styrene/acrylonitrile copolymer compositions comprising binary blends ofstyrene/acrylonitrile copolymers and butyi acrylate/aerylonitrilecopolymers. in another aspect, this invention relates to methods formaking binary blends of styrene/acrylonitrile copolymers and butylacrylate/ acrylonitrile copolymcrs.

Copolymers of styrene with acrylonitrile. especially those containingfrom 90 to 50 parts by weight styrene and. correspondingly. from toparts by weight acrylonitrile. constitute an important class ofcommercial resins. finding widespread use as injection molding material.Unfortunately. styrene/acrylonitrile copolymers of this type have verylimited flexibility. in fact. they are comparatively brittle materialswhich do not show a definite yield point. The tensile elongation of suchstyrene/acrylonitrile copolymers isof the order of only a few percentand the flexural deflection is very small. Thus. manystyrene/acrylonitrile copolymers lack toughness. Although plasticizerscan be used to improve the toughness of styrene/acrylonitrileeopolymers. the plasticized copolymer invariably has a low heatdistortion point or softening point which restricts its use. and theplasticizcrs tend to exude from the copolymer over a period of time.

We have discovered that improved styrene/acrylonitrile copolymercompositions can be obtained by blending into said styrene/acrylonitrilecopolymers a small amount of a butyl acrylate/acrylonitrile copolymer.

An object of this invention is to provide improved styrene/acrylonitrilecopolymer compositions.

Another object of this invention is to provide binary polyblendcompositions of styrene/acrylonitrile copolymer and butylncrylate/acrylonitrile copolymer.

Another object of this invention is to improve the flexural propertiesof styrene/acrylonitrile copolymer compositions without significantlylowering the heat distortion temperature of said copolymer compositions.

Other aspects. objects. and advantages of this invention will beapparent from a consideration of the accompanying disclosure and theappended claims.

in accordance with this invention, improved styrene/ acrylonitrilecopolymer compositions are made by incorporating small amounts of butylacrylate/acrylonitrile copolymer in said styrene/acrylonitrile copolymerto form a binary polyblend of the same. The novel binary polyblendcompositions of this invention comprise a major proportion of astyrene/acrylonitrile copolymer and a minor proportion of a butylacrylate/acrylonitrile copolymer. Ordinarily. the binary polyblendcompositions of this invention comprise from about 1% by weight to about10% by weight butyl acrylate/acrylonitrile copolymer and the remainderstyrene/acrylonitrile copolymer. Preferably. the styrene/acrylonitrilecopolymer polyblend compositions of this invention contain from 2% byweight to 7% by weight of the butyl aerylate/acrylonitrile copolymer.Although the above stated proportions give useful as well as preferredcompositions, other compositions outside the stated proportions can alsobe formed with fewer improvements in physical properties and with im-"ice provements to a lesser degree than are obtained in theabove-disclosed composition.

The binary styrene/acrylonitrile copolymer composttions of thisinvention can be prepared by either mechanical methods or bypolymerization methods to produce polyblends having a high degree ofhomogeneity. In the mechanical method, the styrene/acrylonitrilecopolymer and the preformed butyl acrylate/acrylonitrile copolymer areintimately admixed together on a conventional mixing machine of the typenormally used for mixing rubber or plastics, e.g., a mill rolls, anextruder, or a Banbury mixer. Preferably. the styrene/acrylonitrilecopolymer is first placed on the mill rolls and, after a small rollingbank has formed in the nip of the rolls, the butyl acrylate/acrylonitrile copolymer is added. if desired, the styrene/ acrylonitrilecopolymer and the butyl aerylate/acrylonitrile copolymer, each indisintegrated or divided form, can be admixed together to form a crudeadmixture which is then placed on the mill rolls. Regardless of themethod by which the mixing of these polymers is accomplished, it isnecessary that they be admixed together or worked under a suihcicnt heatand pressure to insure an efficient dispersion of the butylaerylate/acrylonitrile copolymer in the styrene/acrylonitrile copolymerso as to form a completely homogeneous material. The temperature atwhich this working or mastication is conducted is not critical so longas the temperature is at least above that where thestyrene/acrylonitrile copolymer fuses and not above the temperaturewhere decomposition sets in. Usually a temperature above about 300 F. or325 F. and less than about 350' F. or 375 F. is sufficient to obtain anadequately intimate combination of the materials. if desired. suitableminor ingredients can also be included in the binary polyblendcompositions of this invention. including such ingredients as fillers,dyes. pigments. stabilizers. and the like.

in the polymerization method of preparing the binary polyblendcompositions of this invention, the preformed butylacrylate/acrylonitrile copolymer is admixed in the styrene andacrylonitrile monomers and the resulting material subjected topolymerization. For best results, this polymerization is carried to ahigh conversion, such as greater than conversion to high molecularweight styrene/acrylonitrile copolymer. In preparing such apolymerization blend, the butyl ncrylate/acrylonitrile copolymer shouldbe thoroughly and intimately dispersed in the monomeric styrene and theacrylonitrile prior to the polymerization.

The foregoing procedures are used by way of example and variouscombinations of the same. or other procedures, can be employed to form abinary blend composition containing a large proportion ofstyrene/acrylonitrile copolymer and a minor proportion of butylaerylate/aerylonitrile copolymer. The preferred method for preparing thebinary polyblend compositions of this invention is by mechanicallymixing the preformed polymer. It will be understood in thisspecification and claims that the term "blend" and "polyblend" as usedherein include both mechanical blends and blends prepared bypolymerizing styrene and acrylonitrile in the presence of preformedbutyl acrylate/acrylonitrile copolymer.

The copolymers of styrene/acrylonitrile used in the novel polyblendcompositions of the invention include eopolymers wherein styrene andacrylonitrile are the sole monomers subjected to copolymerization, aswell as copolymers prepared from comonomers which also contain otherpolymerizable unsaturated comonomers in an amount preferably notexceeding l5 wt. percent of the total comonomers of styrene andacrylonitrile. Examples of such polymerizable unsaturated comonomerswhich may be present include tit-methyl styrene, vinyl toluene, ethylacrylate, butyi acrylate, methyl methacrylate, and the like. Thestyrenc/acrylonitrilc copolymcr produced, even if other polymerizablcunsaturated comonomers are present, should have a high molecular weight.The styrene/ acrylonitrile copoiymers used in this invention comprisefrom 90 to 50 parts by weight styrene and, accordingly, from to 50 partsby weight acrylonitrile; however, other styrcne/acrylonitrilc copolymcrcompositions outside this range can also be used with less advantageousresults.

The styrene/acrylonitrile copolymers employed in the binary polyblcndcompositions of this invention are commercially available products andcan be made by any of the well known styrene/acrylonitrileeopolymerizatlon techniques from monomeric material comprising styreneand acrylonltrile either with or without butyi acrylate/ acryionitrilecopolymcr present. One common technique is mass polymerization whereinthe only material present in the reaction mixture is the monomer plusany catalyst and any modifier that may be used to effect the molecularweight, plus butyi acryiate/acrylonitrile copolymcr if it is to beincorporated during the polymerization, and no added solvent or otherreaction medium is present. Suitable catalysts for use are those thatpromote free rcdicals, e.g., pcroxy type and azo type catalysts.Examples of such catalysts include bcnzoyi peroxide, ditertiary butyiperoxide, diaeetyl peroxide, dimcthyl phcnyl hydroperoxymethane, ande,s'-azo-bisisobutyronitriie. 'Ihc copolymcrization can also be effectedby the solvent copolymcrization technique which is similar to the masspolymerization technique except that a solvent for the mono mers and/orpolymers is also present during the polymerization. The copoiymerizationcan also be effected advantageously by suspension or emulsionpolymerization techniques. Each of these techniques involves the use ofa non-solvent for the monomer and polymer, but in the suspensiontechnique the particles of monomer and ultimately the polymer arecomparatively large, while in the emulsion procedure the particles arequite small and the product is a stable latex. For suspensionpolymerization, a reaction medium such as water is used together with asmall amount of a suspending agent, for example, tricalcium phosphate, avinyl acetate-malcic anhydride copolymer product, or the like, to give asuspension of particles in the initial reaction mixture which are not ofsuiilcicntiy small size as to result in a permanently stable latex asproduct. To effect emulsion polymerization, a suiiicicnt amount ofemulsifying agent, for example, a water-soluble salt of a sulfonatedlong-chain alkyl aromatic compound. is employed in suitable quantityalong with vigorous agitation whereby an emulsion of the reactants isformed and the product is obtained in the form of a latex. The latex canthen be coagulated if desired by known methods and the polymer separatedfrom the water. In those embodiments of the invention wherein styreneand acrylonitriie are copolymerized in the presence of preformed butyiacrylate/acrylonitrile copolymcr, the preformed polymer may tend to makeit more difficult to form an emulsion than in the case of the monomersalone. However, the emulsion technique has certain advantagesparticularly in that a very rapid and complete conversion to a highmolecular weight product is obtained. Conventional recipes andprocedures for effecting mass, suspension and emulsion copolymerizationof styrene with acryionitrlle are so well known to those skilled in theart that they need not be reiterated here. Emulsion and suspensionpolymerization can be effected at temperatures which are chosen inaccordance with the catalyst system used but which may. for example. befrom 50' C. to 100 C. Mass polymerization is usually most advantageouslyeffected at temperatures within the range of 25 C. to 123' C.

The butyi scrylstc/seryioaitriie oopolymers utilized in the binarypolyblend compositions of this invention are prepared by copolymcrizingbutyi acrylate with aerylonitrile. For use in this invention, the butyiaerylate/acrylonitrile copolymcr should contain a large proportion ofbutyi acrylate and a minor proportion of acrylonitrilc. Preferably, thebutyi acrylatc/acrylonitrile copolymcr employed in this invention isprepared from an admixture of monomers comprising from by weight to byweight butyi acryla-te and correspondingly from 15% by weight to 5% byweight acrylonitrile. However, butyi acrylate/acrylonitrile copolymcrscontaining proportions of monomers outside this range can also be usedif desired, but usually with icss advantageous rcsulLs.

The butyi acrylatc/ncrylonitrile copolymcrs for use in this inventionare commercially available products. Examplcs of some commerciallyavailable materials include "Lactoprcne UN" and Acrylon llA-l2." Methodsfor preparing the copolymers of butyi ncrylate and aerylonitrile arewell known to those skilled in the art and any such methods may be usedfor preparing such copolymcrs for use in this invention. Thus, butyiacryiate and acryl onitrile can be copolymcrizcd using the mass,suspension or emulsion polymerization techniques although it ispreferred to prepare the copolymcr in an emulsion polyrn erizationsystem. In the emulsion polymerization procedurc, polymerization of thebutyi acrylate and acryl onitrilc comonomcrs is effected in the presenceof water and which contains dissolved therein a suitable catalyst and anemulsion stabilizing agent. Examples of suitable catalysts includeammonium pcrsulfatc, benzoyl peroxide, hydrogen peroxide, sodiumpcrborate, and other water soluble salts of pcroxy acids. The quantityof the pet'oxy compounds used as catalysts may be from about 0.02 to2.0% by weight of the polymcrizabic compounds. The emulsion stabilizingagent may be any of the wide variety of wetting agents, which are ingeneral organic compounds containing both hydrophobic and hydrophilicradicals, for example, sodium alkyl sulfate, sulfatcd aromatic otheralcohol, sodium alkyl aryl sulfonate, fatty alcohol sulfate, sorbitantriolcatc, and the like. Ordinarily. the emulsion polymerization isconducted at a temperature in range of from 65' C. to 95' C. dependingupon the nature of the polymerization system and the particular catalystused.

The styrenc/acrylonitrile and butyi acrylate/acrylonitrile copolymcrpolyblcnds of this invention, prepared as described herein, can alsohave included therein addi tional materials such as plasticizers,stabilizers, fillers, dyes, pigments, other polymers. and the like.These matcrials can be added to the preformed styrcne/acrylonitrilecopolymcr and the preformed butyi acrylate/acrylonitrile copolymcr bymilling together or otherwise mixing the added materials with thecopolymcrs, or can similarly be added to the blends of styren-/acrylonitrilc copolymcr with butyi acrylatc/acrylonitrile copolymcr,or can be present during the polymerization of styrene and aerylonitriiemonomers containing preformed butyi acrylatc/ acrylonitrile copolymcr,provided that such presence doesnot adversely affect the polymerizationprocess and prodnets to an undesirable extent.

The advantages, desirability and usefulness of the pres-1,

ent invention are illustrated by the following example.

EXAMPLE Styrcne/acryionitrile copolymcr polyblcnds containing. varyingproportions of butyi acryiate/acrylonitrile coi polymer were prepared bymechanically milling the various admixtures on a 3" x 8" Thropp millrolls at l74' C. A rough mix was first prepared from the preformed polymers in powdered or pelleted form in a stainless steel beaker and thenthis rough mix was placed on the heated mlll rolls and thoroughlyhomogenized by intensive hot milling for 5 minutes or until an adequatedispersion was obtained. The blends were then sheeted and stripped fromthe mill rolls. After sutilcient cooling. the sheets were cut into i to2 inch squares for convenient feeding to an Abbe grinder for grindinginto pellet size for injection molding on a one ounce Watson-Stillmanmachine.

The physical properties of the blends were then determined on theinjection molded samples and are reported in Table I. These propertieswere determined according to the standard ASTM procedures, morespecifically, tensile strength and elongation were determined accordingto ASTM D-882-46, flexural strength and deflection were determinedaccording to ASTM D-79049T, and Notched impact strength was determinedby the Izod method as set forth in ASTM D-256-47T.

Table I composition comprising a mechanical blend of a major proportionof a styrene/acrylonitrilc copolymer of high styrene content and a minorproportion of a butyl acrylate/acrylonitrile copolymer of high butylacrylate content.

2. A styrene/acrylonitrile copolymer binary polyblend compositioncomprising styrene/acrylonitrile copolymer of high styrene content andfrom 1% to by weight PROPERTIES OF BTYRRNEIACRYLONITRILE COPOLYMER ANDDUTY! ACRYLATI'ZI ACRYLONITRILE COI'OLYMEN. POLYBLENDB Composition,percent Tensile Properties Flesttral Properties Notched lltttyl YieldFailure impact Styrene! Aerylait-I Strength. Deflection, Strength,Aeryionilrlle Aery p.s.l. int-hes it.-lh./ln. Copolymer trite Co-Btrenath, l-.lnnr.. Btreaath, Elena polymer I p.s.l. percent p.s.t.permit i 0 11.400 1.8 18.374 0.24 0.1m 07.0 2.6 time 0.? 7.070 20.4 90.50.3l 0.01 06.0 8.0 l0.t477 0.7 0.000 15.0 21.017 02!) 0.4 90.0 100 0.10.0)0 0.l 18.340 0.80 0.33

d kl'ltltklglk C-ll type styrenelsarylonltrile copolymer containing72 1. percent styrene and as wt. percent a y l r e.

I Act lon ilA-l'l type hutyl aeryialeltsrrylonltrlle copolymercontaining as wt. percent buts-l aerylate and I: as percentacrylonitrile.

The data in Table l clearly shows the improvement in flexibility to beobtained by blending a small amount at butyl acrylatc/acryionltriiecopolymer into a styrene/ ncrylonitriie copolymer obtained from amixture of monomers comprising 72% by weight styrene and 28% by weightacrylonitrile. For example, the ilexural deilcction of thestyrene/acrylonitrile copolymer was increased from 0.24 inch to a valuegreater than 0.80 inch, the limit of the particular test equipment used.by blending in amounts of butyl acrylatc/acrylonitrile copolymercomprising 5.0 wt. percent and 10.0 wt. percent of the polyblend. Also.the addition of butyl acrylate/acrylonitrite copolymer in an amount assmall as 2.5 wt. percent of the blend increased the tensile elongationat failure of the styrcne/acrylonitriie from 1.8% to 20.4%. Similarly,5.0 wt. percent of the butyl acrylate/acrylonitriie copolymer raised thetensile elongation at failure to 15.0%. in addition. 2.5% by weight and5.0% by weight of the butyt acryiate/acrylonitrile copolymer raised thetlexural strength of the styrene/acrylonitrile copolymer from 18.374p.s.i. and 21.047 p.s.i.. respectively. These improvements in theilexurai properties of the styrene/ acryionitrile copolymer wereobtained with little adverse nilcct on the Notched impact strength ofthe styrene/ acryionitriie copolymer and. in fact. improved the Notchedimpact strength somewhat at the lower concentrations of butylnerylate/aerytonitrile copolymer.

The binary polyblend compositions obtained had very outstanding physicalappearance. being clear in appearnncc. and could be readily lalectlonmolded to obtain products having good surface gloss. The polyblendcompositions oi this invention can also be subiccted to compressionmolding and other operations which are standard forstynene/acrylonitriie eopolymers. These polyblends can be used to makemolded structures as well as plastic sheets suitable for cutting orotherwise converted to an intended use. They can also be mixed withother materials. such as pigments. plasticizers. natural and syntheticresins, litters and the like. according to procedures well known tothose sltilled in the art.

Reasonable variation and modification of the invention as described arepossible. the essence of which is that there have been provided binarypolyblend compositions ot styrcne/acryionitrlie copolymer andbutylacrylate/acrylonitrlle copolymer comprising a major amount of astyrene/aeryionitrlle copolymer, and methods for preparing the same.

We claim:

1. A styrene/aeryloaitriie copolymer binary polyblend iii) of a butylacrylate/acrylonitriie copolymer of high butyl acrylate content.

3. A styrenc/acryionitrile copolymer binary polyblend compositioncomprising styrene/acrylonitrile copolymer and from 1% to 10% by weightof a butyl acryiatc/acrylonitrile copolymer, said styrene/acrylonitrilecopolymer comprising a major proportion of styrene and a minorproportion 01 acrylonitrile and said butyl aerylate/acrylonitritecopolymer comprising a major proportion of butyl acrylate and a minorproportion of acrylonitrile.

4. A styrene/acrylonitrile copolymer binary polyblend compositioncomprising a mechanical blend of a major proportion of astyrenc/acrylonitrile copolymer containing from 50% to 90% by weightstyrene and correspondingly from 50% to 10% by weight aeryionitrilcbased on the weight of comonomers polymerized, and a minor proportion ofa butyl acrylate/acryionitriic copolymer containing from to 95% byweight butyl acrylate and correspondingly from 15% to 5% by weightacrylonitrile based on the weight of comonomers polymerized.

5. A styrene/acrylonitrile copolymer binary polyblend compositioncomprising a mechanical blend of styrenc/ acryionitrile copolymercontaining from 50% to by weight styrene and correspondingly from 50% to10% by weight acrylonitrile. based on the weight of comonomcrspolymerized. and butyl acrylate/acrylonitrile copolymer containing 88.0%by weight butyl acrylate and 12.0% by weight acrylonitrile. based on theweight of comonomers polymerized.

6. A styrenc/acryionitrile copolymer binary polyblend compositioncomprising 97.5% by weight of a styrene/ acryionitrile copolymercontaining 72% by weight styrene and 28% by weight acrylonitrile. basedon the weight of comonomers polymerized. and 2.5% by weight butyl acryhate/acrylonitrile copolymer containing 88% by weight butyl acryiate and12% by weight acrylonitrile, based upon the weight of comonomerspolymerized.

7. A styrene/acryionitrile copolymer binary polyblend compositioncomprising by weight of a styrene/ acrylonitriie copolymer containing72% by weight styrene and 28% by weight acrylonitrile. based upon theweight of the comonomers polymerized. and 5.0% by weight butylacrytate/acrylonitriie copolymer containing 88% by weight butyl acryiateand 12% by weight acrylonitrile. based upon the weight of comonomerspolymerized.

8. A styrene/acrylonitrite copolymer binary polyblend compositioncomprising 90.0% by weight of a styrenc/ acrylonitrlle copolymercontaining 72% by weight styrene and 28% by weight acrylonitrile, basedupon the weight of the comonomers polymerized, and 10.0% by weight butylacrylate/acrylonitriie copolymcr containing 88% by weight butyl acrylnteand 12% by weight acrylonitrile, based upon the weight of comonomerspolymerized.

9. A method for preparing a binary polyblend composition of astyrene/acrylonitrile copolymcr and a butyl acryiate/aerylonitrilecopolymcr, said method comprising mechanically admixing preformedstyrene/acrylonltriio copolymcr containing 72% by weight styrene and 28%by weight ncrylonltrile, based on the weight of comonomers polymerizedwith 2.5% by weight butyl acrylnte/aerylonltrile copolymcr.

l0. A method for preparing a binary polyblend composition of astyrene/acrylonitrile copolymcr and butyl ncrylate/acrylonitrilecopolymcr. said method comprising mechanically admixing preformedstyrene/acrylonitrile copolymcr containing 72% by weight styrene and 28%by weight acrylonitrile, based on the weight of comonomers polymerized.with 5.0% by weight butyl aerylate/acrylonitrile copolymcr.

ii. A method for preparing a binary polybiend composition ofstyrene/acrylonitrile copolymcr and butyl acrylate/acryionitrilecopolymcr, said method comprising mechanically admixing preformedstyrene/acrylonitrile copolymcr containing 72% by weight styrene and 28%by weight acrylonitrile based on the weight of comonomers polymerized,with 10.0% by weight butyl aerylate/acrylonitrilc copolymcr.

12. The method for preparing a binary poiyblend composition of astyrene/acrylonitrile copolymcr of high styrene content and a butylncrylatc/ncryionitrile copolymcr of high butyl acryiate content, saidmethod comprising admixing a mnior proportion of saidatyrene/ncrylonitrllo copolymcr with a minor proportion of said butylacrylnte/aerylonltrile copolymcr.

References Cited in the file of this patent UNITED STATES PATENTS 202,646,417 Jennings July 2!, 1953 2,958,670 Hare Nov. 1, 1960 3,04l,307Baer June 26, 1962

1. A STYRENE/ACRYLONITRILE COPOLYMER BINARY POLYBLEND COMPOSITIONCOMPRISING A MECHANICAL BLEND OF A MAJOR PROPORTION OF ASTYRENE/ACRYLONITRILE COPOLYMER OF HIGH STYRENE CONTENT AND A MINORPROPORTION OF A BUTYL ACRYLATE/ACRYLONITRILE COPOLYMER OF HIGH BUTYLACRYLATE CONTENT.